Integrated analysis reveals the effects of substituting pea with mung bean on microbial succession and metabolite profiles during medium-temperature Daqu fermentation.

Daqu serves as the saccharifying and fermenting starter in Baijiu production, yet the effects of raw material variation on community succession and metabolite formation during fermentation remain unclear. In this study, amplicon sequencing and metabolomic profiling were applied to compare mung bean Daqu (MBQ), produced by substituting pea with mung bean, with traditional medium-temperature Daqu. Microbial succession patterns were largely conserved after mung bean substitution, whereas stage-specific differences were observed in community composition, environmental associations, and microbial co-occurrence patterns. MBQ was enriched in thermotolerant spore-forming bacteria, particularly Kroppenstedtia, and functional fungi, including Thermomyces, Saccharomycopsis, and Aspergillus. These microbial differences were associated with higher saccharification, liquefaction, and fermentation powers at different stages. Spearman correlation analysis revealed distinct microbe-metabolite associations in MBQ involving pyrazines and plant-derived secondary metabolites. MBQ showed higher accumulation of higher alcohols during the middle stage, particularly phenylethyl alcohol (1.05-23.02 mg/kg), exclusive detection of 2,5-dimethylpyrazine and 2-ethylpyrazine, and flavonoid-related non-volatile metabolite profiles. These findings provide new insights into how raw material variation is associated with microbial succession and metabolic features during Daqu fermentation.